Active load circuits with current-to-voltage transfer stages, also known as transimpedance stages, convert an output current typically generated by a voltage-to-current transfer stage, also known as transconductance, back into a voltage. These circuits are used, for example, in the area of analog electrical circuit topologies for application specific integrated circuits (ASICs) manufactured in process technologies that provide bipolar transistors, or enhancement mode MOS transistors, or both in the case of BiCMOS technologies.
Where a voltage amplifier is necessary in an analog signal processing chain internal to the ASIC or at the interface between the ASIC and its environment, it is desirable to provide a low impedance at the amplifier's output node. This has the benefit of an output voltage that is independent of the characteristics of the load impedance. For integrated circuits that operate at low supply voltages, it is important to have circuit topologies that provide sufficient output voltage swing without requiring a lot of "headroom". The additional supply voltage necessary to operate the circuit should be small compared to the voltage swing available at the output.
If the integrated circuit is used for battery operated portable devices, such as cellular telephones, mobile communication devices, etc., the requirements of high voltage efficiency and low output impedance should be met with the minimum amount of supply current possible. In general, circuit topologies that perform impedance transformation to lower impedances require a significant amount of supply current.
The present invention is directed to overcoming one or more of the problems discussed above, in a novel and simple manner.